1. Field of the Invention
The present invention relates to a glass composition, a glass frit, a dielectric composition and a multilayer ceramic capacitor using the same, and more particularly to a borosilicate system glass frit, which has high specific surface area, excellent high temperature fluidity and high solubility for BaTiO3, a composition thereof, a dielectric composition containing the same and a multilayer ceramic capacitor using the same.
2. Description of the Related Art
Recently, along with rapid development in electric and electronic appliances for miniaturization, light weight, high performance and so on, multilayer ceramic capacitors used therein are also facing demands for smaller size and larger capacitance. In order to realize smaller size and larger capacitance, dielectric layers of such a multilayer ceramic capacitor are getting thinner while being stacked by a greater number. At present, BaTiO3 dielectric layers are stacked by 470 layers or more with a thickness of 3 μm or less in order to realize a capacitor having an ultra high capacitance. Occasionally, a dielectric layer having a thickness of 2 μm or less is also demanded. In order to produce such a multilayer ceramic capacitor having an ultra high capacitance with a greater number of dielectric layers stacked on atop another, it is critical to make the dielectric layers as thin as possible. As the dielectric layers are getting thinner, a uniform micro-structure has become the most important factor to ensure in order to realize dielectric characteristics and reliability.
In addition to thin dielectric layers, continuity of internal electrodes also act as a very important factor to ensure in order to realize the capacitance of a multilayer ceramic capacitor. Ni electrode layers generally used for internal electrodes have a sintering temperature lower for about several hundred ° C. than that of ceramic dielectric material. Thus, sintering performed at a too high temperature increases the sintering shrinkage difference between the internal electrode layers and the dielectric layers, thereby causing delamination. Furthermore, heat treatment (sintering) performed at a high temperature leads to quick conglomeration of the Ni electrode layer, thereby causing electrode discontinuity. This as a result degrades capacitance while increasing short ratio. Therefore, in order to prevent such problems, it is preferable to sinter the Ni internal electrodes and the ceramic dielectric layers at a low temperature of 1,100° C. or less in a reducing atmosphere.
Furthermore, multilayer ceramic capacitors need a thermally stable capacitance in order to achieve high quality performance. The multilayer ceramic capacitors, according to their use, are required to satisfy X5R dielectric characteristics defined by the Electronic Industries Alliance (EIA) standard. According to this standard, capacitance variation (ΔC) should be ±15% or less at a temperature ranging from −55° C. to 85° C. (reference temperature 25° C.).
As conventional sintering agents used for fabrication of multilayer ceramic capacitors, BaO—CaO—SiO2 system glass frit and BaSiO3 system mixture powder are typically used. However, such sintering agents rarely promote sintering at a low temperature of 1,150° C. or less owing to their high melting point of 1,200° C. or more. Furthermore, such a conventional vitreous sintering agent accelerates liquid formation at a high temperature, which disadvantageously narrows a sintering temperature range for the fabrication of a multilayer ceramic capacitor. Japanese Patent Application Publication No. 2000-311823 discloses (Ba, Ca)xSiO2+x, where x=0.8 to 1.2, as a sintering agent for the fabrication of a multilayer ceramic capacitor. However, dielectric layers containing such sintering agent disclosed in this document have a sintering temperature exceeding 1,100° C. Thus, with the sintering agent disclosed in this document, it is difficult to produce a multilayer ceramic capacitor having ultra thin dielectric layers.